1. Field of the Invention
This invention relates to a press-fit structure of a shaft which is suitably used for a press fit of, for example, a rotor and a shaft of a cooling medium compressor of an automotive vehicle air conditioner, and which is constructed as such that a press-fit crack can be prevented from occurring and a torque can be surely transmitted.
2. Description of the Prior Art
For example, a rotor of a cooling medium compressor which is installed in an air conditioner of an automotive vehicle and a shaft for securing the rotor, are, in general, integrally fitted together by means of press-fit. In recent times, lightness of a cooling medium compressor is pointed out as one way for improving a fuel consumption of an automotive vehicle, and there appears a cooling medium compressor, in which the rotor is made of a light weight material such as aluminum alloy and the shaft is made of a steel material.
However, in a press-fit structure including a shaft and a rotor which are made of such materials as mentioned, since a thermal expansion coefficient of the rotor member is larger than that of the shaft member, a slippage is occurred in the press-fitting portions during a driving of the cooling medium compressor and a sure transmission of a torque is often disturbed.
In order to overcome the above-mentioned trouble, it is thinkable that, for example, a press-fit width is made wide or a press-fit length is made long. In that case, however, the rotor is likely to break at the press-fitted portion and therefore, this solution is unemployable.
A known art for solving the above problem is disclosed, for example, in Japanese Patent Eraly Laid-open Publication No. 59(1984)-68586. More specifically, this publication teaches a process for manufacturing a cooling medium compressor comprising pressurizing a side surface of a rotor made of an aluminum alloy in the axial direction, inserting a rotor material corresponding to a recess formed in the rotor by means of the pressure into a roulette groove formed in the peripheral surface of a shaft made of an iron-contained material, and securing both of them together, thereby to press fit the shaft into a shaft hole of the rotor.
However, in this conventional manufacturing process, since the shaft of the roulette groove is annularly formed in the circumferential direction of the shaft, a critical value of slippage is low with respect to a shaft torque and therefore, an anxiety towards an occurrence of slippage of the shaft cannot be wiped out. Moreover, since the so-called plastic fluid method is used in the above-mentioned process, a pressing machine having a large capability, etc. are required, which results in a large sized apparatus. Moreover, since the rotor material is limited to a soft material, a wear-resistance is poor. Thus, this process is difficult to be put into actual practice.